1. Field of the Invention
The invention relates to systems that automatically control the temperature of an object being heated, and more particularly to a method and apparatus for controlling a movable energy source when it is being operated to heat the surface of an object.
The invention is applicable to controlling a spatial movement of localized energy sources such as electron, ion, laser or plasma beams and electric arc as well. The invention can find use in metallurgy for melting, ingot pulling and zone-type cleaning; in mechanical and instrument engineering; in welding, mechanical treatment and heat treatment; in microelectronics; in vacuum film deposition methods and apparatus, in microtreatment and the like.
2. Description of the Prior Art
Known in the art is a method for controlling electron beam heating, wherein an electron beam is caused to be rotated along the circumference of a circle of a given radius that is adjusted by varying the amplitude of sine sweep voltages and the velocity of movement of the electron beam is adjusted by varying the oscillation frequency of a sine voltage. An apparatus to realize the described method comprises two phase shifters, an adder, three amplifiers, and a double amplitude limiters. The sine voltages that are 90.degree. out of phase with respect to each other are applied, via matching amplifiers, to the deflection system of an electron gun.
Known in the art is another method for controlling electron beam heating, wherein an electron beam is caused to pass over the predetermined locations on an object and is held immovable for a certain time interval at each such location. An apparatus for carrying out this method comprises two locked-on generators providing step voltages and coupled to the deflection systems of an electron gun.
Known in the art is a method and apparatus for automatic control of the heating mode of an electronic thermal installation. In accordance with the method, the power of the electron beam is adjusted by varying the power delivered to the cathode of the electron gun with the help of a Hall sensor that reads the beam power. The apparatus comprises a Hall sensor, a comparison unit and a regulator that controls the power fed to the cathode of the electron gun.
The above-mentioned methods and apparatus are disadvantageous in that they do not provide for a correction of the movement and power of the energy source, which is necessary to compensate for a deviation in the distribution of the temperature measured on the surface of an object from a preset distribution.
There is a method for controlling electron beam heating, which method is realized by virtue of an apparatus providing for controlling the electron beam heating mode of a furnace (cf. the USSR Inventor's Certificate No. 418,836 dated Aug. 2, 1972).
The known method comprises the steps as follows: measuring the temperature of the surface of an object by means of a scanning pyrometer that receives pertinent data in passing along the predetermined path on the object surface; obtaining a signal representative of a difference between the measured and the preset temperature of the object surface and remembering that signal; varying the power and movement of the energy source along the predetermined path in accordance with the signal representative of the temperature difference.
An apparatus to realize the above-described method comprises a temperature pickup to sense the temperature on the surface of an object and a scanning unit which constitute together a scanning pyrometer with a deflection system, a temperature setter adapted to set a temperature to which the object is heated, a comparison unit adapted to compare the predetermined and the measured temperature, control units adapted to control the movement of the energy source relative to rectangular axes, and memory units to store the signals representative of the predetermined and measured temperature.
In the described method and apparatus, the same path is used along which the energy source (electron beam) is moved and along which the temperature on the surface of the object is measured. Note that the same signal provides for the displacement of the energy source and for the scanning movement of the pyrometer, that signal being formed on the basis of the signal representative of the difference between the predetermined and measured temperature. As a result, the temperature pickup for sensing the temperature on the object surface can be implemented only as a camera tube with electronic scanning. This in turn imposes limitations on the described method and apparatus since the present-day temperature sensors with optical/mechanical scanning feature higher accuracy.
In addition, the most useful applications of the described method and apparatus are concerned with the case where the movement of the energy source and, therefore, the path along which the temperature is measured are one-dimensional; on the other hand, sufficient difficulties arise when the energy source is caused to move along an arbitrary path on the object surface. Finally, it is not possible to utilize the described method and apparatus in the case where the path along which the energy source is moved and that along which the temperature is measured do not coincide with each other or in the case where the temperature is to be measured concurrently at several points on the object.